How do reproductive strategies and sexual selection shape animal behaviour?
Sex and behaviour: r and K reproductive strategies, parental investment, mating systems, intra- and inter-sexual selection, mate choice and courtship, sexual dimorphism, and alternative reproductive behaviours.
An SQA Advanced Higher Biology answer on sex and behaviour, covering r and K reproductive strategies, parental investment, mating systems, intra- and inter-sexual selection, mate choice and courtship, sexual dimorphism, and alternative reproductive behaviours such as sneaker males.
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What this key area is asking
The SQA wants you to explain how reproductive strategies and sexual selection shape behaviour: the r and K continuum, parental investment, the main mating systems, intra- and inter-sexual selection, mate choice and courtship, the resulting sexual dimorphism, and alternative reproductive behaviours.
Reproductive strategies: r and K
Parental investment
Sexual selection
Mate-choice criteria include physical condition, secondary sexual characteristics, courtship quality, territory and the promise of parental care, all of which can indicate a male's fitness.
Mating systems
Alternative reproductive behaviours
Examples in context
Example 1. The peacock's tail. Peahens prefer peacocks with larger, more symmetrical trains, an honest signal of health. This inter-sexual selection has driven an exaggerated, costly male trait, a classic case of sexual dimorphism produced by mate choice.
Example 2. Sneaker salmon. Small "jack" salmon mature early and sneak fertilisations while large males fight, a sneaker strategy maintained by frequency-dependent selection. The example shows an alternative reproductive behaviour coexisting with the dominant one.
Try this
Q1. State which sex is usually the choosier and why. [1 mark]
- Cue. The sex with higher parental investment, usually the female, because each offspring costs it more.
Q2. Explain what is meant by sexual dimorphism. [2 marks]
- Cue. Consistent differences in size, appearance or behaviour between males and females, often produced by sexual selection.
Exam-style practice questions
Practice questions written in the style of SQA exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
SQA AH style4 marksCompare r-selected and K-selected reproductive strategies, giving the type of environment each suits.Show worked answer →
A 4-mark answer needs both strategies and their environments.
An r-selected strategy produces many offspring with little or no parental care; many die, but a few survive. It suits unstable or unpredictable environments where rapid reproduction exploits short-lived opportunities.
A K-selected strategy produces few offspring with high parental investment, so most survive to maturity. It suits stable or crowded environments near the carrying capacity, where competition is strong and quality matters more than quantity.
Markers reward (1) r-selected makes many offspring with little care, (2) suiting unstable environments, (3) K-selected makes few offspring with high investment, and (4) suiting stable or crowded environments.
SQA AH style3 marksExplain how parental investment can lead to female mate choice and sexual dimorphism.Show worked answer →
A 3-mark answer needs the investment difference, the choosiness and the consequence.
Females usually invest more in each offspring, through larger gametes and often parental care, so each reproductive event is more costly to them and their number of offspring is more limited.
Because their investment is high, females are selective and choose males showing signs of high fitness, while males compete for these choosy females.
This inter-sexual selection by females, and intra-sexual competition between males, drives the evolution of exaggerated male traits, producing sexual dimorphism.
Markers reward (1) females invest more per offspring, (2) so they are choosy and select fit males, and (3) sexual selection produces dimorphism.
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Sources & how we know this
- SQA Advanced Higher Biology Course Specification — SQA (2019)